1. Field of the Invention
This invention generally relates to a data communication system having a unit time period for allowing to carry out data communication, such as a pay public telephone system, and, in particular, to a data communication apparatus, such as a facsimile machine, suitable for use in such a data communication system.
2. Description of the Prior Art
Typically, a time limited data communication system with or without wire includes, for example, a public pay telephone system using coin or a card and a multi-access channel (MCA) system. The former is the case with wire and the latter is the case without wire. In such a data communication system, the connection is forcibly disconnected when a predetermined unit time period for communication has elapsed. For example, as well known, in the case of a pay public telephone system, a unit time period for communication is predetermined and a total length of time capable of keeping communication alive depends on the total amount of money accumulated by depositing one or more coins. In this case, if the remaining time has reached a predetermined value, a warning audible signal is supplied to a receiver held by the user. In this case, if an additional one or more coins are deposited, the communication time period is extended depending again on the amount of money thus deposited. If no additional coins are deposited, then the connection is automatically disconnected when the time period determined by the deposited coins has elapsed.
A facsimile machine may be used as a terminal in such a public pay telephone system. In this case, however, there is a chance that the connection is disconnected automatically while the communication is still in progress, e.g., while one of a plurality of pages of original documents is being transmitted. If this happens, then the operator must go through the calling and connecting procedure again in order to transmit the remaining pages. This procedure would involve transmission of the telephone number of the destination terminal by dialing or pressing buttons, setting of the remaining originals to be transmitted, and setting of transmission conditions, such as line density. Such a retransmitting procedure is quite cumbersome to the operator, and it is also possible that various errors could occur because the operator is require to exercise various cares. Therefore, there has been a need to provide an improved data communication system and a terminal for use therewith, which allows the user to transmit desired information without any problem and with ease, reliability and high efficiency, even if communication is automatically discontinued when an allowable communication time period has elapsed.